<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
    <style>
        #box{
            width:100px;
            height:100px;
            background-color:blue;
        }
    </style>
</head>
<body>
<div id="box"></div>
</body>
</html>